Our earlier U.S Pat. No. 6,104,355 describes an antenna with a loading coil lying in a frame, with vibration of coil turns being avoided by a plurality of adhesive fixing strips that fix the separation of coil turns. Applicant finds that after the coil is wound, it may deform during handling, and this requires careful tuning of each unit by stretching or squeezing its length, before applying the fixing strips. The need for such tuning increases the cost of manufacture. The loading coil should be of minimum weight, since it lies at the top of an upstanding base. An antenna with a loading coil that could be manufactured at low cost while assuring repeatable precise location of the coil, in a construction of minimum weight, would be of value.
In accordance with one embodiment of present invention, an antenna loading coil is provided, which enables rapid manufacture while assuring predetermined axial spacing of the coil turns, assuring a predetermined diameter of the coil, and assuring location of the coil concentric with the axis of the frame while keeping the coil turns spaced from the side walls of the frame. The loading coil includes at least three members that each have slots that closely receive the turns, with the rib members circumferentially spaced about the axis. A spacing ring that is coupled to the upper ends of the rib members, pushes apart the rib members to slightly expand the diameter of the upper end of the coil. The lower ends of the rib members are mounted on a lower end of the frame at a fixed spacing from the frame axis by abutment of shoulders of the rib members and of the frame lower part. The coil has upper and lower connection ends to which termination lugs are crimped and soldered, for easy mounting of the coil. The wire of the coil is formed of a copper tube instead of solid copper.
The novel features of the invention are set forth with particularity in the appended claims. The invention will be best understood from the following description when read in conjunction with the accompanying drawings.